Engines may increase output power by using boosting devices that compress intake air. Since charge compression increases air temperature, charge air coolers may be utilized downstream of a compressor to cool the compressed air, further increasing the potential power output of the engine. As intake air passes through the charge air cooler and is cooled below a dew point, condensation occurs. The condensate may be accumulated at a trap and delivered to the engine subsequently, e.g., during steady-state or cruise conditions, at a controlled rate of ingestion. However, because the ingested water slows the rate of combustion, even small errors in the introduction of water into the engine can increase the likelihood of misfire events. Engine control systems may employ various misfire control approaches to reduce misfires causes by the ingestion of water.
One example approach for addressing moisture induced misfires is shown by Tonetti et al. in EP 1607606. Therein, an intake air flow rate is adjusted based on an oxygen concentration of recirculated exhaust gas to compensate for condensate in the EGR. Another example approach is shown by Wong et al. in U.S. Pat. No. 6,748,475. Therein, a fuel injection and spark timing is adjusted based on a parameter indicative of an oxygen concentration or water concentration of recirculated exhaust gas. This allows misfire events arising during steady-state conditions due to a sudden ingestion of too much water or condensate to be reduced. Even when the amount of water ingested is small, during a transient tip-in from steady state conditions, such as when going from low to moderate air mass flow rates to high air mass flow rates, the ingested water can cause slow combustion issues. In particular, the high mass flow rate can break the surface tension of the condensate, and release from the charge air cooler where the engine ingests it in larger quantities.
However the inventors herein have identified potential issues with such an approach. As one example, even with adjustments to intake air flow rate, fuel injection, and/or spark timing, misfires caused due to condensate ingestion during steady-state conditions may not be sufficiently addressed. Specifically, engine combustion stability during steady-state conditions may be very sensitive to the amount of condensate. Consequently, even small errors in condensate metering can lead to misfires.
In one example, some of the above issues may be addressed by a method for a boosted engine comprising: increasing airflow through a charge air cooler in response to a deceleration event. In this way, condensate can be purged without incurring misfire events.
As one example, an engine controller may deliver condensate collected at a charge air cooler to an engine during a deceleration event. For example, in response to a tip-out, when the engine is spinning un-fueled (e.g., during a deceleration fuel shut off or DFSO event), a valve coupled to the charge air cooler (or coupled between the charge air cooler and the intake manifold) may be opened so that the condensate can be introduced into the engine's intake manifold. Additionally or optionally, an intake throttle may be opened to increase airflow to the engine. By opening the valve and/or throttle during the deceleration, intake manifold vacuum generated from the spinning engine may be advantageously used to draw in the condensate. Additionally the engine could be downshifted to a lower gear, further increasing engine speed (and air mass flow rate), thereby creating additional vacuum force to evacuate the condensate.
A timing of opening the valve and/or throttle may be coordinated with a timing of the deceleration event such that the valve is opened at the same time as cylinder fueling is shut off The valve and/or throttle may then be closed when sufficient condensate has been purged or when cylinder fueling is resumed (e.g., during a tip-in following the tip-out). In this way, by delivering condensate from a charge air cooler to an engine during a deceleration event, the large amount of intake manifold vacuum generated from the engine braking can be advantageously used to draw condensate into the engine. By delivering the condensate to the engine during conditions when cylinder combustion is not occurring, the condensate can pass through the engine system without degrading combustion stability. Further, since the condensate is introduced while no combustion is occurring, concurrent engine actuator adjustments for misfire control may not be required. Overall, a larger amount of condensate may be purged into the engine without increasing engine misfires.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.